This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Induction tools are used in the oil and gas industry to determine the resistivity of earth formations and reservoirs surrounding a borehole. Induction tools work by using a transmitting coil (transmitter) to set up an alternating magnetic field in the earth formations. This alternating magnetic field induces eddy currents in the formations. One or more receiving coils (receivers), positioned at a distance from the transmitter, are used to detect the current flowing in the earth formation. The magnitudes of the received signals are proportional to the formation conductivity. Therefore, formation conductivities may be derived from the received signals.
However, heterogeneities in the formation complicate the derivation of formation conductivity from the received signals. One prevalent complication that affects the derivation of formation conductivity from the received signals arises from the presence of conductive fluids in the borehole surrounding the induction instrument. This is referred to generally as the borehole effects. Often, the fluids in the borehole (drilling mud) are made very saline, thus conductive, as part of the drilling practice. The conductive drilling muds can contribute a significant proportion of the received signals and, therefore, should be carefully removed, minimized, or corrected.
The borehole effects upon the measurements of an induction tool may be further magnified when used within a borehole of a well containing water-based mud (WBM), as opposed to oil-based mud (OBM). Oil-based mud may have a high resistivity compared to that of water-based mud. For example, oil-based mud may have a resistivity of about 1,000 ohm-meter, or even higher values, whereas water-based mud may have a resistivity as low as about 0.1 ohm-meter, or even lower values. The high resistivity for the oil-based mud has only a small borehole effect on the measurements of the induction tool as the fluids within the borehole have high resistivity compared to the water-based mud. On the other hand, the low resistivity of the water-based mud increases the borehole effects upon the measurements of the induction tool. Accordingly, there continues to be a need to improve the reliability of the measurement of induction tools, particularly when used within wells containing water-based mud.
The illustrated figures are only exemplary and are not intended to assert or imply any limitation with regard to the environment, architecture, design, or process in which different embodiments may be implemented.